Subcutaneous tetrahydrobiopterin (a cofactor in monoamine synthesis) was administered to 5 patients with dementia of the Alzheimer type. No gross change in neurologic examination or significant adverse effects were observed. Cerebrospinal fluid (CSF) drug and monoamine metabolite concentrations were evaluated. Intravenous haloperidol (a dopaminergic antagonist) was administered to 5 healthy subjects to test the dopamine system in aging. No significant adverse effects were seen. Plasma haloperidol and prolactin concentrations and quantitative cognitive and motor tests were evaluated. Oral debrisoquin was administered to 9 healthy subjects to assess central nervous system dopamine activity in relation to aging. Adverse effects were recorded (nausea, anorexia) in 1 patient. Plasma and urine monoamine metabolites will be analyzed.